Do not show chat button for apple or outlook address book contacts, even if the appropriate operation set is supported, until our user interface start handling external source contact chats properly.

src/net/java/sip/communicator/impl/gui/main/contactlist/ContactListTreeCellRenderer.java

@@ -634,8 +634,12 @@ private void initButtonsPanel(UIContact uiContact)
         else
             statusMessageLabelHeight = 15;
 
-         UIContactDetail imContact = uiContact.getDefaultContactDetail(
-             OperationSetBasicInstantMessaging.class);
+        UIContactDetail imContact = null;
+        // For now we support instance messaging only for contacts in our
+        // contact list until it's implemented for external source contacts.
+        if (uiContact.getDescriptor() instanceof MetaContact)
+            imContact = uiContact.getDefaultContactDetail(
+                         OperationSetBasicInstantMessaging.class);
 
         if (imContact != null)
         {